Conventionally, micro electro mechanical systems (MEMS) which have an exciter configured to include a piezoelectric thin film provided on an Si semiconductor layer are known. For example, Patent Literature 1 discloses a vibrating device wherein one ends of a plurality of vibrating arms are each connected to a supporter. In this vibrating device, the vibrating arms have each an Si semiconductor layer, and an SiO2 film is provided on the Si semiconductor layer. On the SiO2 film, a first electrode, a piezoelectric thin film, and a second electrode are laminated in this order. More specifically, the exciter including the piezoelectric thin film is constituted on the Si semiconductor layer. The vibrating device disclosed in Patent Literature 1 uses bulk waves.
Since the exciter is provided on the Si semiconductor layer, a vibrator with a high Q value can be constituted. In the vibrating device disclosed in Patent Literature 1, an SiO2 film with a relatively large thickness of 2 μm or more is provided to improve temperature characteristics.
Disclosed in Patent Literature 2 is a surface acoustic wave semiconductor device including an n-type Si substrate doped with P. It is said that elastic coefficients and velocities of surface acoustic waves can be changed by using the n-type Si substrate doped with P and the temperature characteristics can be improved thereby.    Patent Literature 1: U.S. Pat. No. 8,098,002    Patent Literature 2: Japanese Patent Laid-Open No. 57-162513